Abstract

Mixed Fe/Co oxide nanoparticles, diameter 8 nm, were prepared using the protein ferritin as a template and characterized by transmission electron microscopy(TEM) and Raman spectroscopy. We show that the latter effectively distinguishes between magnetite (Fe3O4), maghemite (γ-Fe2O3) and Co ferrite (CoxFe3-xO4). Zero-field-cooled susceptibilitymeasurements show isolated magnetite nanoparticles have a blocking temperature TB = 18 ± 1 K, but that adding 0.5% Co raises TB to 30 K. Data for thermal relaxation from saturation obey a T ln(t/τ0) scaling, enabling us to determine the energy barrier distributions for the dispersed nanoparticles. For Fe oxide only a single peak was found. However, with the addition of only 0.5% Co a second component is observed that decreases rapidly with increasing energy.

Received 11 October 2011Accepted 09 November 2011Published online 05 March 2012

Acknowledgments:

This work was supported by the EU 7th Framework Project Grant Agreement no.228673 (MAGNONICS) and the UK Engineering and Physical Sciences Research Council. It was carried out with the support of the Bristol Centre for Nanoscience and Quantum Information (NSQI).

Key Topics

[Magnets or magnetic bodies characterised by the
magnetic materials therefor; Selection of materials for their magnetic
properties, Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties]